One method of ascertaining the quality of a diffusion-bonded weldment requires the measurement of the weldment's thickness. This measurement can be undertaken as shown in FIG. 1, which illustrates a caliper 2 having anvils 4 and 6 measuring the total thickness of two bonded components 8 and 10 together with the weldment 12 contained between them. Comparison of this total measured thickness with the measured total thickness of the two components without the weldment, prior to bonding, will allow a computation of the thickness of the weldment by subtraction. As will now be discussed, accurate measurement requires accurate positioning of the anvils 4 and 6 with respect to the components 8 and 10. Such positioning is commonly called fixturing.
If one of the components has a rough surface, such as the surface of a metallic casting taken directly from a sand mold, problems arise in the thickness-measuring procedure. One problem is illustrated in FIG. 2, which shows two possible positions of the anvil 6 of FIG. 1, but in enlarged form and labeled as 6A and 6B. The surface 9 of the component 10 is rough and, as the alternate positions 6A and 6B of the anvil 6 indicate, the measured thickness of the components 8 and 10 in FIG. 1 will depend upon the anvil position chosen. Thus, the measured thickness has no absolute definition.
Further, even if no absolute measurement is sought, but only a relative comparison of two successive measurements, problems arise. Accurate comparison requires that the anvils 4 and 6 be positioned exactly in the same position, such as the position 6B for anvil 6, for both measurements. This is difficult to achieve.
Still further, it is possible that the components 8 and 10 may become nicked or scratched between measurements. If a scratch occurs at the location where the anvil 6 contacts the component, random error is introduced. All of these problems are worsened when the components 8 and 10 are of irregular shapes, as are sand-cast gas turbine engine blades.